Abstract:

A process for making a stimuli responsive liquid crystal-polymer composite
fiber comprising mixing a liquid crystal, a polymer, and a solvent;
processing the mixture in the presence of an electric potential across a
collection distance; phase separating a polymer and said liquid crystal;
and encapsulating said liquid crystal within said polymer. The fiber
generally comprises a liquid crystal core and a polymer shell wherein the
liquid crystal is responsive to chemical changes, thermal and mechanical
effects, as well as electrical and magnetic fields. A liquid crystal
containing fiber can be utilized as optical fibers, in textiles, and in
optoelectronic devices.

Claims:

1. A process for forming a liquid crystal containing polymer fiber,
comprising the steps of:mixing at least one liquid crystal, one or more
at least semi-transparent polymers, and at least one solvent, and forming
a mixture;processing said mixture in the presence of a voltage
differential applied across a collection distance;phase separating said
polymer from said liquid crystal; andencapsulating said liquid crystal
with said polymer.

2. The process of claim 1, wherein said liquid crystal comprises an
nematic liquid crystal, a cholesteric liquid crystal, a smectic liquid
crystal, a liquid crystal comprising a bent-core molecule, a lyotropic
liquid crystal, a columnar mesophase liquid crystal, or a discotic liquid
crystalline porphyrin, or any combination thereof; and wherein at least
50% of light incident upon said polymer is transmitted there through
according to ASTM-D1003.

3. The process of claim 2, wherein the weight of said liquid crystal is
from about 10% to about 90% by weight based upon the total weight of said
at least one liquid crystal and said one or more polymers; and wherein at
least about 60% of incident upon said polymer is transmitted there
through according to ASTM-D1003.

5. The process of claim 4, wherein the weight of said liquid crystal is
from about 40% to about 80% by weight based upon the total weight of said
at least one liquid crystal and said one or more polymers; wherein the
weight of said solvent is from about 1 to about 95% by weight based upon
the total weight of said at least one liquid crystal, said one or more
semi-transparent polymers, and said solvent; wherein said solvent is a
ketone, chloroform, dimethylfurane, tetrahydrofuran, dimethyl formamide,
an alcohol having from 1 to about 9 carbon atoms, an amide having from 2
to about 15 carbon atoms, water, an organic acid having from 1 to about
10 carbon atoms, an alkane or a halogenated alkane having from 6 to about
11 carbon atoms, and any combination thereof; and wherein the amount of
said solvent is from about 60% to about 95% by weight based upon the
total weight of said at least one liquid crystal, said one or more
semi-transparent polymers, and said solvent.

6. The process of claim 5, wherein said polymer is a polyacrylate,
polyurethane, polycarbonate, polyester, polylactic acid, or poly(methyl
methacrylate), or any combination thereof; and wherein at least about 80%
of light incident upon said polymer is transmitted there through
according to ASTM-D1003.

7. The process of claim 1, wherein the amount of said voltage differential
is from about 5 to about 50 kilo volts; and wherein said collection
distance is from about 1 to about 100 cm.

8. The process of claim 5, wherein the amount of said voltage differential
is from about 10 to about 30 kilovolts; and wherein said collection
distance is from about 3 to about 25 cm.

9. The fiber diameter of claim 1, wherein the diameter of said fiber is
from about 10 nanometers to 1 millimeter.

10. The fiber diameter of claim 4, wherein the diameter of said fiber is
from about 100 nanometers to about 100 microns.

11. The fiber diameter of claim 8, wherein the diameter of said fiber is
from about 250 nanometers to about 10 microns.

17. A process for making a liquid crystal-polymer composite fiber,
comprising the steps of:forming a composition comprising a mixture of at
least one liquid crystal, one or more at least semi-transparent polymers,
and a solvent, wherein said one or more polymers are partially or fully
dissolved by the solvent, said liquid crystal exceeding its solubility
limit in said polymer; andelectrospinning the composition and forming a
fiber having a shell comprising the one or more polymers and a core
comprising the at lease one liquid crystal.

[0002]Liquid crystals are soft matter systems in which strongly
anisometric liquid crystal molecules display long-range orientational
order, but possess partial or no long-range positional order. The
anisotropic optical properties of liquid crystals are also the basis for
their large birefringence. In addition, liquid crystal molecules possess
anisotropic electric and magnetic susceptibilities and the orientation of
liquid crystals can be changed by external stimuli, such as electric and
magnetic fields. Therefore, these advanced materials have been
extensively utilized in variety of display applications.

[0003]The liquid crystal/polymer composites of various types represent an
important and broad class of three-dimensional structures utilized at the
forefront of flexible liquid crystal display science and technology.
Polymer dispersed liquid crystals and polymer stabilized liquid crystal
systems may be given as the classical examples for the use of liquid
crystal-polymer composite structures in display applications. In liquid
crystal-polymer composites, the polymer component serves a number of
critical functions: provides mechanical support (ruggedness); determines
the thermomechanical stability of the composite; protects the device or
fiber functionality from environment; helps to distribute the applied
pressure by acting as a stress transfer medium (self-sustaining);
provides durability, interlaminar toughness and
shear/compressive/transverse strengths to the system in general, and
maintains the cell gap of the device. Therefore, synthetically produced
polymeric materials have been the key component toward producing
self-sustaining and self-adhering flexible display prototypes.

[0005]Polymeric fibers can be formed by a range of methods including melt
spinning, melt blowing, wet spinning, gel spinning, dry-jet wet spinning,
dry spinning and electrospinning. The method of fiber formation is chosen
based on the properties of the polymer and the dimensions and physical
properties desired in the final fibers. Secondary components including a
second polymer or small molecule components can be incorporated into the
fibers during the spinning process either as mixtures with the main
polymer or in separate domains by methods known to those versed in the
art of fiber spinning. Methods for forming bi-component fibers include
coaxial spinning or extrusion and spontaneous phase separation during the
spinning process.

[0007]It is, therefore, an object of present invention to produce a
composite liquid crystal-polymer fiber by a) mixing at least one liquid
crystal, one or more at least semitransparent polymers, and at least one
solvent, b) processing said mixture in the presence of an voltage applied
across a collection distance, c) phase separating said polymer from said
liquid crystal, and d) encapsulating said liquid crystal with said
polymer.

[0008]The fibers of the present invention comprise a polymer shell and a
liquid crystal core that possess stimuli responsive electro-optical
properties that are retained within the constrained geometry of the
fiber. The polymer-liquid crystal composite fibers can be prepared via
electrospinning. The diameter of the liquid crystal composite fiber
ranges from about 10 nanometers to about 1.0 millimeter. These fibers are
prepared by means of a high electric field gradient generated between a
charged polymeric fluid and a collection plate. The encapsulated liquid
crystal fibers of the present invention can be stimulated by an
electrical field, a magnetic field, and to a lesser extent by thermal or
photonic radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is an illustration of typical electro-optical responses of
the fibers upon application of an electric field under crossed
polarizers; (a) and (c) show the applied voltage pulses of 120 V; (b) and
(d) are the electro-optical curves of electrospun 5CB/PLA fibers,
respectively; (b) show the response upon removal of the field; and (d)
shows the response when the field is applied.

[0010]FIG. 2 is an illustration of the response time characteristics of
the fibers, where time ON is t4-t3 and time OFF is t2-t1; ΔI is the
difference between maximum and minimum intensity.

[0011]FIG. 3 is an illustration of response time characteristics as a
function of an applied voltage for electrospun 5CB/PLA fibers.

[0012]FIG. 4 is an illustration of the field-induced light transmission
characteristics of the fibers; Imin is obtained at the "ON" state when
the field is applied and Imax is obtained at the "OFF".

[0013]FIG. 5 is an illustration of the relative contrast ratio as a
function of an applied voltage of the liquid crystal fibers.

[0016]FIG. 8 is a POM image of PLA/5CB fibers (a) at nematic phase (below
TNI) and (b) at isotropic phase (above TNI). Inset scale bars
refer to 20 μm. A 50× objective was used. FIG. 8(c) relates to
video frames showing isotropic to nematic phase transition of 5CB in PLA
fibers (5CB/PLA), 58/42 wt %). These images were captured by MGI Video
Wave 4 Software under the crossed polarizers during cooling of the
sample. The bright region of the fibers (1) is at the nematic phase and
the dark region of the fibers (2) is at the isotropic phase.

[0017]FIG. 9 is a POM image of a single PLA/5CB fiber collected at 6 cm,
0.6 mL/h, and 15.5 kV. Arrows 1 and 2 show the well-aligned 5CB molecules
at the defect-free sites of the fiber, while arrow 3 indicates the
Schlieren liquid crystal texture at the beaded part of the fiber. FIG.
9(b) relates to the electrospun 5CB/PLA fibers as seen under POM. 9(c)
shows the fibers rotated 45° with respect to polarizer (P) and
analyzer (A). Fibers shown from 1 to 4 by an arrow show a couple of
examples for alignment sensitive light polarization characteristics of
the fibers.

[0020]FIG. 12 is a (a) Picture of oriented pure PLA fibers collected onto
an aluminum grid. (b) Picture of oriented PLA/5CB fibers shown between
crossed polarizers. (c) POM image of oriented PLA/5CB fibers shown in
(b), where the average direction of the long axes of fibers N is located
45° to crossed polarizers. (d) The image shown in (c) is rotated
where N is oriented along the polarizer. A 5× objective is used.

[0021]FIG. 13 is a POM images of PMMA/5CB liquid crystal fibers shown
between (a) crossed polarizers and (b) parallel polarizers, where a
10× microscope objective is used. The same fibers are seen with
50× microscope objective where the images are taken under (c)
crossed polarizers, (d) the polarizer is placed 75° to the
analyzer, and (e) parallel polarizers. These fibers are collected at 0.25
mL/h, 8 cm, and 14 kV.

[0022]FIG. 14 is a a) POM images of PLA/cholesteric liquid crystal fibers
collected at 0.6 mL/h, 8 cm, and 9 kV. POM images are taken with a
20× microscope objective under a) crossed polarizers in the
reflective mode, b) crossed polarizers in the transmissive mode, c)
parallel polarizers in the transmissive mode. The fibers images are also
taken with a 50× microscope objective under d) crossed polarizers
in the reflective mode, e) crossed polarizers in the transmissive mode,
f) parallel polarizers in the transmissive mode.

[0025]FIG. 17 is a typical structure for a core/shell liquid
crystal-polymer composite fiber, where the cross section of the fiber is
shown and the composite fiber comprises a) a polymer shell and b) a
liquid crystal core layer. The liquid crystal core can be composed of
small molecule liquid crystal materials or liquid crystalline polymers.

[0026]FIG. 18 is another embodiment of the core/shell liquid
crystal-polymer composite fiber, where the cross section of the fiber is
shown and the composite fiber comprises a) an outer polymer shell, b) a
middle polymer shell or a liquid crystal core layer, and (c) a core
polymer shell or a liquid crystal core layer. The liquid crystal core can
be composed of small molecule liquid crystal materials or liquid
crystalline polymers. Polymer material in the fiber composition can be
chosen from a wide range of polymers listed in claims. Liquid crystal
phase can be chosen from numerous compounds set forth below.

[0027]FIG. 19 is an example for multiple stacking of liquid
crystal-polymer fibers. A cross sectional view is shown. The composite
fiber comprises a) a polymer shell and b) a liquid crystal core layer.
The liquid crystal core can be composed of small molecule liquid crystal
materials or liquid crystalline polymers. More complex arrangements of
the fibers can be acquired by assembling them in various arrays or
packing orders.

[0028]FIG. 20 is another embodiment for the core/shell liquid
crystal-polymer composite fiber, where the cross section of the fiber is
shown and the composite fiber comprises a) an outer polymer shell, and b)
several inner or islands of liquid crystal cores. The shape and the
number of core islands can be modified based on the application or by
fiber processing parameters. Some of the core islands can be composed of
various types of liquid crystalline polymers. The liquid crystal core can
be composed of small molecule liquid crystal materials or liquid
crystalline polymers. Polymer material in the fiber composition can be
chosen from a wide range of polymers set forth below and the liquid
crystal phase can be chosen from numerous compounds set forth below.
Black areas represent the polymer shell, whereas gray areas represent
islands of polymer and/or liquid crystal materials.

DETAILED DESCRIPTION OF THE INVENTION

[0029]The fibers of the present invention containing one or more liquid
crystals encapsulated within a shell made from one or more polymers are
derived by a process wherein initially the one or more polymers but not
necessarily the one or more liquid crystals are soluble or substantially
soluble in one or more solvents. Such liquid crystals are known to the
literature and to the art and generally include various mesomorphic
compounds as either small molecule liquid crystal compounds or liquid
crystal polymers.

[0031]The one or more polymers utilized to form the shell of a fiber are
generally at least semi-transparent so that light incident upon the shell
can be transmitted therethrough. By the term "at least semi-transparent"
it is meant that at least about 50%, desirably at least about 60% or at
least about 70%, and preferably at least about 80% or at least about 90%
of light incident upon the polymer is transmitted therethrough in
accordance with ASTM-D1003.

[0034]The relative amounts by weight of the one or more liquid crystals
and the one or more polymers can vary with respect to each other with
preferably the amount of the liquid crystals being a majority. The weight
amount of the one or more liquid crystals can generally range from about
10% to about 90%, desirably from about 25% to about 85%, and preferably
from about 40% to about 80% by weight based upon the total weight of the
one or more liquid crystals and the one or more polymers. Naturally the
amount by weight of the one or more polymers is the remaining percent by
weight to add up to one hundred percent.

[0035]On occasion, if the liquid crystal and polymer do not degrade upon
formation of a fiber as by electrospinning, then no solvent need be
utilized. That is, in one embodiment, the amount of solvent is 0% by
weight. However, an important requirement of the present invention is
that very likely one or more solvents are utilized to dissolve the
polymer but not necessarily the liquid crystal component of the mixture.
Solvents are generally organic compounds and include various ketones such
as acetone and methyl ethyl ketone; chloroform; dimethylfuran and
tetrahydrofuran (THF); various alcohols having from 1 to about 9 carbon
atoms such as methanol, ethanol, propanol, hexafluoro 2-propanol, and
isopropanol; various amide compounds having from 2 to about 15 carbon
atoms, such as N,N-dimethylformamide (DMF); and N,N-dimethyl acetamide
(DMAc); water, various organic acids having from 1 to about 10 carbon
atoms, such as formic acid and trifluoroacetic acid; various alkanes or
halogenated alkanes having from about 6 to about 11 carbon atoms, such as
dichloromethane, heptane, and hexane; mixtures thereof; and the like. The
amount of the solvent can range widely with respect to the total weight
of the one or more liquid crystals, the one or more polymers and the one
or more solvents. Such solvent amounts are generally from about 1% to
about 95% by weight, desirably from about 40% or about 60% to about 95%
by weight, and preferably from about 80% to about 95% by weight based
upon the total weight amount of the one or more liquid crystals, the one
or more polymers, and the one or more solvents.

[0036]The liquid crystal-polymer mixture can be processed by
electrospinning the mixture. Upon spinning the various mixtures of the
liquid crystal and/or the liquid crystal polymer, and the light
transparent shell polymer will separate and form different phases with
the shell polymer encapsulating the liquid crystals.

[0037]Electrospinning is a method known to the art and to the literature
and a general description thereof is set forth in U.S. Pat. No.
6,753,454; in WO 2005/024101 A1, in "Polymer Nanofibers Assembled by
Electrospinning", Frenot et. al, Current Opinion in Colloid and Interface
Science 8(2003), 64 75; and in "Nanostructured Ceramics by
Electrospinning", Ramaseshan et al, Journal of Applied Physics 102,111101
(2007); all of which are hereby fully incorporated by reference. An
example of an electrospinning device is schematically shown in FIG. 6
wherein (a) is a high voltage source that is connected as by wire (b) to
a dispenser for the liquid crystal-polymer solvent mixture such as an
injector or syringe (c). The liquid crystal-polymer-solvent mixture that
is stored in container (d) is pumped therefrom into syringe (c) with a
voltage charge being applied thereto. A voltage differential exists
between injector or syringe (c) and a collection plate (f) (i.e. a
collection distance) that is grounded at (g). In order to obtain suitable
phase separation, a threshold voltage value or differential must be
utilized that is generally 5 kV volts for most mixtures. Generally, the
voltage differential can range from about 10 to about 50, desirably from
about 10 to about 30 and preferably from about 10 to about 25 kV for most
liquid crystal-polymer-solvent mixtures. Upon processing the mixture,
that is ejecting the mixture from the ejector or syringe (c) the solvent
component evaporates with the polymer phase separating from the liquid
crystal and coalescing into a thread-like shape with the polymer coating
or encapsulating the liquid crystal. The in situ formed liquid crystal
core-polymer shell fiber is then collected on collection plate (f). In
lieu of the collection plate, a rotating drum can be utilized whereby the
fiber is wound around the drum. Subsequently, the fiber can be removed
therefrom for various end uses as set forth hereinbelow. The distance
between the tip of the injector or syringe and the collection plate or
rotating drum is generally from about 1 to about 100 centimeters,
desirably from about 3 to about 25 centimeters, and preferably from 5 to
about 20 centimeters. The thickness of the fiber will vary and can be
controlled by various factors such as the diameter of the injector
through which the liquid crystal-polymer-solvent mixture is extruded or
ejected, by the amount of the solvent contained within the mixture, and
by the collection rate if a rotating drum is utilized whereby the fiber
is drawn. The thickness of the liquid crystal encapsulated fiber can vary
as from about 10 nanometers to 1.0 millimeters, desirably from about 100
nanometers to about 100 microns, and preferably from about 250 nanometers
to about 10 microns.

[0038]The collection or target plate can generally be of any size and
shape, and can be flat or for example, in the form of a rotating drum.
The collection plate is electrically conductive and hence made of a
conductive material or have a conductive coating or material thereon.
Suitable collection plates can be made from various metals such as iron,
steel, aluminum, copper, nickel, zinc, and the like. Alternatively, they
can contain a non-conductive substrate and have a conductive coating
thereon such as any of the above noted metals. Suitable substrates
generally include any type of glass or plastic. Moreover, transparent
coating layers can be utilized such as compositions containing
indium-tin-oxide or antimony-tin-oxide. The collection plates can also be
made of conducting polymers such as PEDOT:PSS or
Poly(3,4-ethylenedioxythiophene)poly(styrenesulfone), poly(thiophene)s,
poly(acetylene)s, poly(pyrrole)s, poly(p-phenylene vinylene)s, and also
electrically conducting fabrics such as conducting polymer coated
fabrics, such as poly(pyrrole) coated fabrics as well as fabrics
containing a metal conductor therein such as metal fibers as for example
iron, copper, aluminum, etc.

[0039]Stated in different words, the liquid crystal core-polymer shell
fibers of the present invention can be manufactured by means of a high
electric field gradient generated between a charged polymeric-liquid
crystal-solvent fluid and a collection plate, where the viscosity of the
polymer solution is tuned to form a Taylor cone at and above the
above-noted threshold field. When the applied voltage reaches a critical
value, electrostatic forces overcome the surface tension of the polymer
solution as at a metallic needle tip. As a result, an electrically
charged jet is emanated towards the collection plate. While the jet
elongates towards the target in usually a spiral path as a result of the
electrically driven bending instabilities induced by Coulomb
interactions, the solvent evaporates and electrospun fibers are deposited
as a nonwoven mat. Since the polymer solution is a homogeneous mixture of
the liquid crystal, the polymer, and the solvent, upon electrospinning
and evaporation of the solvent, the liquid crystal phase exceeds its
solubility limit in the polymer and precipitates with the polymer
encapsulating it. The various parameters, such as collection distance,
applied voltage, feeding rate, as well as the material characteristics of
polymers (e.g. molecular structure and weight) and polymer solutions
(e.g. viscosity, conductivity, and surface tension) are used to optimize
the morphology of the electrospun fibers.

[0040]Various additives in effective amounts to achieve one or more
desired properties can be utilized provided that they generally do not
interfere with the formation of a polymeric shell and a liquid crystal
core. Various dyes can thus be utilized such as positive and/or negative
dichroic dyes, photo-reactive dyes, and dopants. Various surfactants such
as one or more cationic, anionic, or nonionic surfactants or mixtures
thereof can be utilized to promote dissolution of the polymer and/or
liquid crystals within the solvent. Various particles, such as
macromolecules and colloidal particles can also be utilized such as
polystyrene, barium titanate, lead zirconate titanate, as well as metals
to improve electrical, thermal, mechanical, and optical properties of the
fibers. Other particles such as generally metal particles can be utilized
to enhance the color of the fibers such as gold, silver, carbon, copper,
chrome, iron, nickel, and zinc particles, and the like, or various
minerals. Colorant dyes can also be utilized such as various azo dyes and
fluorescent dyes that are known to the art and to the literature. Often
it is desirable to utilize various adhesives to increase adherence of the
fibers with regard to various substrates or other fibers. Other additives
include one or more biological materials that can be utilized
incorporated onto or within the fiber such as chemical markers,
membranes, proteins, nucleic acids, cellular components, tissues. Still
another class of additives that can be utilized comprise quantum dots and
C-dots.

[0041]The invention will be better understood by reference to the
following examples which serve to illustrate, but not to limit the
present invention.

[0046]The electrospun composite fibers of PLA/5CB were prepared as
follows. First, PLA and 5CB of 42/58 weight percent were mixed together,
and chloroform/acetone solvent (3:1 volume ratio) was added later. The
PLA/5CB/solvent mixture was stirred on a heating plate (Fisher Model
210T) for a day at room temperature. The concentration of PLA in
chloroform/acetone solvent was 7.3 wt % for the samples. Next the polymer
solution was drawn into the syringe and injected with a metal needle
using a syringe pump. Both pure PLA and PLA/5CB fibers were electrospun
with a metallic needle of 24 gauge (0.41 mm in diameter). The electric
potential difference (10 kV-22 kV), the collection distance (6 cm-16 cm),
and the feeding rate (0.1 mL/h-1 mL/h) were varied to modify the
morphology of the composite fibers.

[0049]A square wave alternating current (AC) electric field was supplied
by a function generator (Hewlett Packard 33120A, 15 MHz) and a wideband
amplifier (FLC electronics F20 AD). An electric field was applied to the
cells via ITO electrodes. The intensity variation was measured through a
photodiode placed at an eyepiece of an Olympus microscope (Olympus, BX60)
by keeping the illumination and the magnification constant. The 10×
microscope objective was used to collect and signal. The optical response
characteristics of the fibers and the voltage pulse were monitored by a
picometer and a PC picometer oscilloscope software from Pico Technology
Ltd. Finally, all the results were digitally saved to the computer.

[0050]Results and Discussion

[0051]Electro-Optical Characteristics of the Fibers Under Crossed
Polarizers

[0052]The LC core in the electrospun 5CB/PLA fibers (58/42 wt %) can be
electrically switched upon application of an AC-electric field. 1 kHz
square waveform was produced repetitively in a burst mode by means of a
function generator. The pulse duration was 100 milliseconds, i.e. the
function generator sends a voltage pulse with a frequency of 1 kHz for a
period of 100 milliseconds and switches off the 100 ms. The amplitude of
the voltage pulse was varied from 0 to 180 V.

[0053]FIG. 1 shows a typical electro-optical response of the fibers at the
voltage pulses of 120 V. FIGS. 1(a) and (c) are the applied square
waveforms, which were monitored by a picometer, and the corresponding
electro-optical responses were obtained from fibers under crossed
polarizers and plotted in FIGS. 1(b) and (d), respectively. FIG. 1(b)
shows the response upon removal of the field. FIG. 1(d) shows the
response when the filed was applied. When the field was applied the
transmitted intensity reaches a minimum value indicating that LC
molecules align along the field and therefore block the transmission of
light.

[0054]When the field was removed, LC molecules realign back to its
equilibrium director configuration in the fiber core that is generally
perpendicular to the polymer surface and light is readily transmitted
through the liquid crystal. Thus, optical microscopy images indicate that
5CB aligns parallel to the surface of PLA. The alignment of 5CB is PLA is
the result of the surface anchoring effect and the polymer structure of
the fiber. In addition, the response characteristics of fibers depend on
liquid crystal material parameters, such as elastic constants, dielectric
constants, and viscosity.

[0055]Time OFF or relaxation time and time ON or switching time values
were calculated based on a 90% change in the light intensity
(ΔI*0.9) and a 10% change in light intensity (ΔI*0.1) as
illustrated in FIG. 2, where ΔI is the difference between maximum
and minimum intensity (ΔI=Imax-Imin). The maximum intensity was
obtained when the field was zero, but the minimum intensity was obtained
when the field was applied. It was observed that switching time values
decrease with increasing applied voltage as suggested by the theory for
polymer dispersed liquid crystal systems (ref: B. Wu, et al., Liquid
Crystals, Vol. 33, Nos. 11-12, 2006, pp. 1315-1322). Moreover, the
relaxation times decline upon removal of field. This indicates the effect
of polymer structure on the reorientation of LC molecules and the
interaction between the polymer sheath and the non-reactive LC molecules.
The degree of interaction and the electro-optical characteristics of
fibers can be modified by changing the polymer type, surface
characteristics, or the type of LC molecule. (ref: R. A. M. Hikmet,
Chapter 3, pp 53, in "Liquid Crystals in Complex geometries", Taylor &
Francis Ltd., 1996, Eds. G. P. Crawford and S. Zumer). FIG. 3 shows the
response time characteristics of the fibers as the magnitude of the field
was changed. As seen, the saturation voltage is about 80 V. The switching
time upon application of 80 V is 4 milliseconds, while the relaxation
time upon removal of the voltage is 13 milliseconds.

[0056]The field-induced light transmission characteristics of the fibers
under crossed polarizers were also studied. From FIG. 4 it can be seen
that the measured maximum and minimum intensity values (arbitrary units)
as a function of the peak voltage amplitude (0 to 180 V) are
significantly different. The relative contrast ratio was also calculated
by dividing the intensity value of the ON state to that of the OFF state
and plotted in FIG. 5. A constant was added to the intensity ratio in
order to offset the curve in the plot. The contrast ratio increases with
the magnitude of the applied field and becomes constant above saturation
voltage 80 V. The transparency of the fibers did not change as the
voltage was increased further.

[0057]In summary, it is apparent that the application of electric field to
the fibers reorients the liquid crystal areas in the fibers. The results
also demonstrate that liquid crystal/polymer fibers can be used as light
modulating fibers upon application of external stimuli.

Example 2

[0058]Electrospinning of PLA/Cholesteric Liquid Crystal Mixture

[0059]The electrospun composite fibers of PLA/cholesteric liquid crystal
were prepared as follows. First, cholesteric liquid crystal mixture was
prepared from E7/CB15/CE2 with a weight ratio of 59/29/12. Next, PLA and
cholesteric liquid crystal was mixed together (45 to 55% by weight
ratio), and chloroform/acetone solvent (3:1 volume ratio) was added
later. The PLA/cholesteric liquid crystal-solvent mixture was stirred on
a heating plate (Fisher Model 210T) for a day at room temperature. The
concentration of PLA in chloroform/acetone solvent was 7.3 wt % for the
samples. Next the polymer solution was drawn into the syringe and
injected with a metal needle using a syringe pump. Both pure PLA and
PLA/cholesteric LC fibers were electrospun with a metallic needle of 24
gauge (0.41 mm in diameter). The electric potential difference (10 kV-22
kV), the collection distance (6 cm-16 cm), and the feeding rate (0.1
mL/h-1 mL/h) were varied to modify the morphology of the composite
fibers. While the flow rate of the polymeric fluid was kept at 0.6 mL/h,
the collection distance and the applied voltage were varied from 6 cm to
16 cm and from 9 kV to 22 kV, respectively.

Example 3

[0060]Electrospinning of PMMA/5CB

[0061]The electrospun composite fibers of PMMA/5CB were prepared as
follows. First, PMMA and 5CB of 50/50 were mixed and DMF solvent was
added later. The PMMA/5CB/DMF mixture was stirred on a heating plate
(Fisher Model 210T) for a day at room temperature. The concentration of
PMMA was 25% by weight in DMF. Next the polymer solution was drawn into
the syringe and injected with a metal needle using a syringe pump.
PMMA/5CB fibers were electrospun with a metallic needle of 24 gauge (0.41
mm in diameter). The electric potential difference (10 kV-22 kV), the
collection distance (6 cm-16 cm), and the feeding rate (0.1 mL/h-1 mL/h)
were varied to modify the morphology of the composite fibers.

[0062]Nematic phase of liquid crystals is one of the mesophases of liquid
crystals without any positional order. The rod-like shaped nematic liquid
crystals, such as 5CB, form an orientationally ordered uniaxial phase
with a unit director n, representing the average direction of the
elongated molecules. The flexible end chains in 5CB allow the molecules
to move around while the rigid core favors alignment. Additionally, in
nematic phase liquid crystals molecules are free to turn about their axis
(continuous rotational symmetry around n). The formation of the liquid
crystal phase for 5CB depends solely on temperature, and these types of
liquid crystals are classified as thermotropic. Therefore, the liquid
crystal properties of composite fibers were determined by observing the
phase transition characteristics of confined 5CB in the fiber. Most
importantly, it was observed that some of the liquid crystal domains
inside the fibers can be electrically switched upon the application of an
AC-electric field.

[0063]The invention will be better understood by reference to FIGS. 6
through 20 wherein the noted polymer encapsulated fibers were made in
accordance with the present invention.

[0064]For electrospinning, first PLA and 5CB were mixed at a 42 to 58
weight ratio, and later, chloroform/acetone solvent (3:1 volume ratio)
was added. The homogeneous solution was obtained by a constant stirring
of the PLA/5CB in chloroform/acetone solvent mixture at room temperature.
Later, this polymer solution was electrospun at room temperature. In
order to compare the effect of 5CB on PLA fiber morphology, pure PLA was
electrospun at identical processing conditions. The illustration of
electrospinning set-up is shown in FIG. 6. The POM image of electrospun
PLA fibers, as shown in FIG. 7a, does not show optical anisotropy
(birefringence), and appears completely dark under crossed polarizers
regardless of the orientation of pure PLA fibers. On the contrary, the
incorporation of 5CB into PLA solution results in the formation of
optically anisotropic and light scattering electrospun liquid crystal
fibers at room temperature (FIG. 7b), indicating that the nematic
mesophase of 5CB is preserved after electrospinning. The beaded fiber
morphology is observed for both pure PLA and PLA/5CB fibers, as shown in
FIGS. 7c and 7d, respectively, where the polarizers are set parallel. The
optical textures within PLA/5CB fibers, in fact, originate from change in
orientation of optically anisotropic rod-like 5CB molecules, which has a
high birefringence of 0.20 at 25° C. In the POM (Polarized Optical
Microscopy) images of PLA/5CB fibers, the spatial variation in light
intensity is the result of the variation in the phase change of light
traversing the sample, where the birefringence of the sample is
integrated over the path of light on the plane of observation. This
physical characteristic of liquid crystal materials allow for the
visualization of the director field n, or the macroscopic molecular
orientation, of the thin films. It is apparent that the composite PLA/5CB
fibers shown in FIG. 7b possess liquid crystal characteristics. The
nematic phase inside the bead structure is also identified from the
optical texture composed of bright and dark brushes with topological
defects, known as Schlieren texture, appearing under crossed polarizers.
In this specific liquid crystal texture, dark brushes appear whenever n
or its horizontal projection orients parallel or perpendicular to one of
the polarizers.

[0065]In order to prove that liquid crystal molecules were confined in the
core of PLA shell fibers, the phase transition from isotropic to nematic
phase was recorded. At 25° C., PLA/5CB beaded fibers exhibit
nematic phase under crossed polarizers, as seen in FIG. 8a. When the
samples are heated up to 45° C. (well above TNI), the optical
anisotropy, and therefore the birefringent texture of nematic phase,
disappears and nematic to isotropic phase transition occurs. In an
isotropic phase, 5CB becomes an orientationally disordered liquid phase
(FIG. 8b). It was observed that the nematic mesophase reformed in the
cavities of PLA on cooling down the sample below TNI. When the
samples were cooled down from an isotropic phase at a rate of 0.1°
C./min, nematic to isotropic phase transition temperatures for pure 5CB
and PLA/5CB fibers were observed at 36.6° C. and 32.8° C.,
respectively. Video frames of the isotropic to nematic phase transition
in these fibers were captured by MGI Video Wave 4 Software and shown in
FIG. 8c during an 18 sec. time interval.

[0066]It is well known that in confined geometries, the alignment of the
nematic liquid crystal depends on the interaction of the liquid crystal
molecules with the confining boundaries. The degree of disturbance of the
director field n varies depending on the anchoring strength of the
surfaces and the boundary conditions in confined geometries. For
instance, planar boundary conditions orient n parallel to the bounding
surfaces. In general, the director configuration of the nematic liquid
crystal inside a few micrometer curved structure of polymer binders is
affected by the elastic forces competing with molecular anchoring at the
surface of polymer. The director configuration of 5CB liquid crystal
constrained in the core of the PLA fibers was studied by analyzing
birefringent textures with POM. For that purpose, a single PLA/5CB fiber
elongated at different directions on the plane of observation was chosen.
As shown POM image of the fiber in FIG. 9, the bright liquid crystal
texture was observed at arrow 1 because n is oriented between crossed
polarizers, while the dark texture at arrow 2 was observed because n is
oriented with the direction of the analyzer. Therefore, the defect-free
part of the cylindrical channels of PLA fibers (<3 μm) clearly
imposes planar or tangential anchoring for 5CB on its surface and aligns
n uniformly along the fiber long axis. On the other hand, the uniformity
of the liquid crystal alignment was altered by increasing the radius of
the cavity (>3 μm) as shown in the beaded part of a fiber (arrow
3), where the orientation of the director field was arbitrary. Randomly
constrained orientational order also leads to the formation of a
Schlieren liquid crystal texture indicating that 5CB molecules are
anchored planar to the surface. FIGS. 9b and 9c also show that the
rotation of the alignment of the 5CB/PLA fibers rotates the polarization
direction of the light under POM. Sample fibers are denoted from 1 to 4.
In FIG. 9c, the sample was rotated 45° with respect to one of the
polarizers. FIG. 9 also shows that light transmission through the fibers
depends on the orientation angles of the polarizers relative to the LC
alignment in the fiber. More detailed information on the electromagnetic
propagation in liquid crystals can be found in various textbooks.
Consequently the uniform alignment of 5CB molecules in the core of the
fibers strongly depends on the size and morphology of PLA fibers.

[0067]It was found that even though the change in the collection distance
(6 cm to 16 cm) did not result in any major difference in fiber size,
shape, and uniformity (not shown), the variation in an applied voltage
(14 kV to 22 kV) altered the morphology of the composite liquid crystal
fibers significantly, as shown in POM images of PLA/5CB fibers (FIG.
10(a-f)) taken with 10× and 50× objectives. For these
samples, the concentration of 5CB, the feeding rate of the polymer
solution, and the collection distance were kept at 58 wt. %, 0.6 mL/h,
and 10 cm, respectively. Particularly, the application of higher voltages
above the threshold voltage (˜14 kV) generated noticeable change in
the size and shape of liquid crystal fibers, as illustrated in SEM images
of the fibers (FIG. 11). The length to width ratio of the beads on fibers
was increased approximately from 2.0 to 4.0 as the applied voltage was
increased from 14 kV to 20 kV. As the applied voltage was raised further
to 22 kV, the beads become very small in size, but the diameters of the
fibers increased significantly to include 58% 5CB in the core of the
fiber, as seen in FIGS. 10c and 10f and FIG. 11c. According to POM
images, the sizes of the some of the fibers are doubled when the applied
voltage was increased from 14 kV to 22 kV (FIG. 10d-f). These results
prove that the size and shape as well as liquid crystal texture in
composite liquid crystal fibers can be modified by changing the
electrospinning parameters.

[0068]Another important aspect of these composite liquid crystal fibers is
the ability to control not only the morphology, but also the average
orientation of the composite liquid crystal fibers. Light modulating
fibers were produced by creating well-oriented composite fibers composed
of PLA and birefringent LCs. This result was achieved by electrospinning
them onto a diamond shape Aluminum collector, between grids, as shown in
FIG. 12a for pure PLA fibers. The spatial arrangements of the average
direction of the long axes of the oriented fibers show some variation due
to the shape of the collector at the edges. Likewise, oriented PLA/LC
fibers were electrospun onto the collector as shown in FIG. 12b between
crossed polarizers. POM images of PLA/5CB fibers in FIG. 12c further
clarify the organization for this new class of composite fibers. In
oriented PLA/5CB fiber arrays, the maximum light intensity was obtained
when the average direction of the long axes of fibers N was set
45° to crossed polarizers (FIG. 12c), while the minimum intensity
was observed if N was oriented along one of the polarizers (FIG. 12d).
Keeping constant the illumination and the 5× magnification, the OM
images of both orientations were computer digitized and normalized (100%
refers to a white image) and the contrast ratio (CR) for the oriented
composite liquid crystal fibers was determined. The CR is defined as the
ratio of the average gray level for the scattering state (FIG. 12c) to
the average gray level for the extinction state (FIG. 12d). The CR value
was calculated as 2.0 for the oriented liquid crystal fibers, where the
average gray levels were 22.2% and 11.1%, respectively. It is apparent
that the bead-free fibers are very sensitive to the polarization
direction of the light. However, the polarization sensitivity of the
composite liquid crystal fiber array lessens because of the residual
light scattering emanating from bead defects located along the fiber long
axis. Consequently, the polarization efficiency of the composite liquid
crystal fibers not only depends on the packing order and the size of the
fiber, but also the morphology of the fiber, the birefringence of the
liquid crystal material, and the degree of orientation of n inside the
fiber. Nonetheless, the results demonstrate that highly oriented
electrospun liquid crystal-polymer fibers can potentially be used as
optical filters or as a scattering polarizer once the structure is
optimized to form defect-free fibers.

[0069]Electrospinning of PMMA/5CB/DMF has resulted in completely different
fiber morphology and liquid crystal alignment in the core of PMMA fiber,
as shown in polarizing optical microscopy images in FIG. 13. FIG. 13a
relates to liquid crystal fibers shown between (a) crossed polarizers and
(b) parallel polarizers, where a 10× microscope objective was used.
The same fibers are seen with a 50× microscope objective where the
images are taken under (c) crossed polarizers, (d) the polarizer is
placed 70° to the analyzer, and (e) parallel polarizers. These
fibers are collected at 0.25 mL/h, 8 cm, and 14 kV. This example shows
that liquid crystal alignment in the cavities of fiber can be manipulated
not only by varying the electrospinning process parameters, but also by
changing the type of polymer. In addition to types of polymer, different
liquid crystal mesophases were tested, such as cholesteric liquid crystal
phase, to obtain different electro-optical effects.

[0070]The cholesteric phase (N*) is a chiral type of nematic phase (N),
where the director field n rotates about the cholesteric helical axis c
with a translation of Pα/2 π. P is called the cholesteric pitch
length, where the director rotates through 2 π radians, and α is
the rotation angle. P is twice the periodicity along the c because n and
-n are indistinguishable. In order to construct a reflective cholesteric
liquid crystal composite fiber, the formation, shape, liquid crystal
texture and orientation of the electrospun fibers were investigated. The
concentration of the cholesteric liquid crystal was kept at 55 wt. % in
PLA solution. Electrospinning process was carried out at room
temperature. It was found that below critical voltage (10 kV), the phase
separation process during electrospinning process resulted in partial
encapsulation of liquid crystal material in the core of the fibers as
seen in FIGS. 14a and 14b. Some of the liquid crystal material was
located at the outside of the fibers. Above 10 kV, the phase separation
process was complete and liquid crystal material was completely
encapsulated in the core of PLA (FIG. 14c). The fiber images were also
taken with a 50× microscope objective under d) crossed polarizers
in the reflective mode, e) crossed polarizers in the transmissive mode,
and f) parallel polarizers in the transmissive mode. The effect of the
applied voltage on the structure of the liquid crystal/polymer composite
fibers is shown in FIG. 15 wherein POM images of PLA/cholesteric liquid
crystal fibers collected at 0.6 mL/h, 16 cm, and at a) 10 kV, b) 18 kV,
and c) 22 kV. POM image of the same PLA/cholesteric liquid crystal fiber
were taken under a crossed polarizer in the reflective mode at: d) 10 kV,
e) 18 kV, and f) 22 kV. A 20× microscope objective is used.
PLA/cholesteric liquid crystal fibers are also collected onto an aluminum
collector to obtained oriented fibers as shown in FIG. 16 between crossed
polarizers.

[0071]Some of the examples for embodiments of core shell liquid
crystal-polymer composite fibers are shown from FIG. 17 to FIG. 20. A
detailed explanation of these examples is set forth below.

[0072]In summary, it was demonstrated that the self-assembly of liquid
crystal molecules occur in the core of the polymer shell containing
fibers at above some threshold voltage. The uniqueness of this system is
that both liquid crystal and polymer components are dissolved in the same
solvent to form a single solution, and concurrently, are electrospun to
form a composite fiber with phase separated hybrid structure. Moreover,
in this structure the liquid crystal component was encapsulated in the
cavities of the polymeric shell with preserved mesophase characteristics.
It is also demonstrated that well-controlled orientation of liquid
crystal composite fibers and size and well-preserved liquid crystal
mesophase core characteristics in specific positions and orientations can
be manufactured via an electrospinning method.

[0073]The fibers of the present invention can be used to produce high-tech
fibers. It is promising that an electrospinning method will pave its way
to create new liquid crystal composite fibers to be constructed as
interactive fabrics. Moreover, the physical and chemical characteristics
of the liquid crystal-polymer fibers can be tailored with additives--such
as dyes, chiral molecules, ferroelectric and ferromagnetic particles,
organic and biological molecules--as well as with other mesophases--such
as bent core liquid crystals, smectic liquid crystals, ferroelectric
liquid crystals, columnar phase forming liquid crystals, and lyotropic
liquid crystals. The optomechanical and optoelectronic properties of the
liquid crystal fibers can also be manipulated by introducing liquid
crystal elastomers into the fiber structure. The inner surface
characteristics of the polymer carrier can also be altered to change
surface anchoring strength and to induce a specific type alignment of
liquid crystal molecules (tangential, tilted, or homeotropic anchoring)
in the core of fiber.

[0074]These bendable liquid crystal-polymer optical fibers and nonwoven
mats can also be engineered to form materials and devices, responding to
chemical changes, thermal and mechanical effects, as well as the
application of electric and magnetic fields. The fibers can be utilized
in variety of photonic applications ranging from optical sensors to light
modulating devices operating in the UV-VISIBLE to IR regions of the
electromagnetic spectra. The polymeric encapsulated liquid crystal fibers
of the present invention can also be utilized as light scattering
polarizers as well as light modulating devices. The fibers of the present
invention can also be further processed or modified to change the overall
functionality of the fiber such as with respect to physical and chemical
characteristics of the surface of the fibers as well as with respect to
fibers having different conductivity, color, shape, air permeability,
luster, repellent or absorbent characteristics, mechanical properties,
and elastic properties. Additionally, the chemistry of the fiber can be
changed to detect other chemicals presents in the surrounding environment
by observing texture, color, or shape changes. Reflective mode of
cholesteric liquid crystal mesophase can also be used to form high-tech
fabrics functioning as a thermo-optic device embedded or woven into
clothing.

[0075]Another important aspect of the present invention is that the fiber
morphology can be chosen to prepare one or more of the following
structures of single or multiple component fibers: hollow segmented pie,
striped polymer core, segmented polymer core structure, metal/polymer
core fiber, concentric ring polymer fiber, sheath/sheath/core polymer
fiber, fibers within fibers, hollow single or multi-component fibers, and
the like. For example, a typical polymeric shell-liquid crystal core is
shown in FIG. 17 wherein the shell is dark annulus (a) and the liquid
crystal core is (b). FIG. 18 relates to a three layer fiber wherein (a)
is an outer polymer shell, (b) is a middle polymer shell or a liquid
crystal core layer, and (c) is a polymer core or a liquid crystal core
layer having a different liquid crystal than that of shell (b). FIG. 19
is an example of multiple polymer shells (a) and liquid crystal cores (b)
arranged in a specific geometric arrangement. Naturally, numerous other
geometric arrangements can be formed utilizing more or less fibers than
depicted in FIG. 19. FIG. 20 is another embodiment wherein several liquid
crystal cores are encapsulated within a single polymer phase as shown.
Once again, several different geometric arrangements can exist utilizing
more or less liquid crystal cores as shown in FIG. 20. Another aspect of
the present invention is that the various one or more polymer
shell-liquid crystal cores can be assembled or woven into several
different configurations, such as one-dimensional, two-dimensional, or
three-dimensional arrangements. The polymeric shell-liquid crystal core
fibers can also be embedded woven, and/or attached to other yarns or
fibers. Moreover, the fibers, either before or after being fabricated or
woven, can have the surface thereof treated with the various organic or
inorganic compounds or layers to change or increase the functionality
thereof such as with respect to thermal, mechanical, chemical, and
electro-optical responses. Still further, the extruded fibers during the
solidification stage are thereafter can be drawn to induce or increase
the strength and/or alignment thereof.

[0076]The molecules of the liquid crystal-polymer fibers of the present
invention possess anisotropic, electrical, and magnetic properties which
render the fibers very useful in a wide variety of end uses. That is, the
amount of light emitted by the liquid crystal containing polymer fibers
of the present invention can be readily controlled by various fields such
as heat, and especially magnetic and/or electrical fields. Thus, the
liquid crystal containing polymer fibers can be utilized as optical
fibers, in textiles, in nonwoven articles, in optoelectronic devices, and
the like. For example the fibers can be utilized in clothes whereupon
entering an electric or magnetic field the fibers will exhibit optical
transmission and/or reflection of light. More practically, an electrical
field can be generated by an electronic device containing batteries in
association with the clothes or the fibers can be placed between two
layers of a photoconductor. The liquid crystal-polymer fibers can also be
used in various magnetic or electrical fields that are programmed to
modulate the amount of light emitted therefrom as for use in various
displays, read out devices, and the like, or as sensors wherein they
detect changes in magnetic and/or electrical fields. When utilized as
sensors, the liquid crystal-polymer fibers of the present invention can
be utilized to detect temperature change in biological and chemical
materials. In addition, the fibers can be used for optical imaging and
recording, mechanical testing of materials under stress, as light
modulators for color electronic imaging, and the like. When necessary the
fibers can be assembled, glued, sprayed, deposited or coated with color
filters, polarizers, retardation plates (compensators), transparent
electrodes, glass or plastic plates and the like.

[0077]The polymer encapsulated liquid crystal fibers of the present
invention can contain various additives therein such as chemical markers,
membranes, proteins, nucleic acids, cellular components, tissues, and the
like with the same being added to the liquid crystal so that during the
formation of polymer encapsulated fibers thereof, the additives will be
contained therein so that composite stimuli responsive fiber materials
and mechanisms can be utilized to develop artificial muscles, optically
responsive membranes, and biological sensors for on-site and lab-based
diagnostic tests for clinical, food, environmental and biosecurity
applications, medical products, dermal applications, and the like.

[0078]While in accordance with the patent statutes the best mode and
preferred embodiment have been set forth, the scope of the invention is
not intended to be limited thereto, but only by the scope of the attached
claims.